The goal of this research is to morphometrically assess normal and experimentally altered cochlear tissues in an attempt to further our understanding of the role of the stria vascularis in auditory dysfunctions. There is some evidence that the stria has an important functional role in the hearing process. Functional and morphological changes of the stria have been observed in human presbycusis and after intense sound exposure and ototoxic drug administration. While pathology of the organ of Corti has been expressed in quantitative terms, little attempt has been made at quantifying stria pathology. The proposed research has four specific objectives: first, to provide normative quantitative data on the chinchilla stria vascularis using morphometric and stereological methods on a large group of animals. Second, to determine whether or not a discrete stria lesion can be produced without producing corresponding hair cell loss. This animal model would allow for future physiological studies of the functional role of the stria. Initial results (using vascular lesions) show that stria damage can be produced without corresponding hair cell loss. Third, to investigate the mechanisms of stria pathology after exposure to a narrow-band sound and surgical puncture of the basilar membrane. These methods will produce localized damage, and the relationship between the acute and chronic phases or stria pathology will be morphometrically assessed. Fourth, to determine (using stereological methods) whether stria cell volume and surface densities are changed after diuretic administration. This experiment should provide an insight into the mechanisms involved in diuretic ototoxicity.